For the fabrication of lenses, hot-pressed glass blanks are normally processed. Such blanks have a shape of flat cylinder disks, or have faces which may be curved, depending on the desired shape for the lens to be produced. In the prior art, the glass blanks are first given the desired contour by means of grinding machines. A first device coarse-grinds the lens blank on one side and provides the blank with a polishable finishing surface in a second operation. The lens is then removed from the first device, turned around, and is also coarse-ground and precision-ground on the other side thereof by a second grinding machine. Then the lens is polished on both sides thereof in a third device. Finally, the rim of the thus polished lens is processed in a fourth device, a so-called centering machine.
The lens rim is provided with a precise circular geometry, possibly also with chamfers at the edges so as to give them a better shock resistance. During the centering operation, the lens is held between metal centering bells which align the lens so that its optical axis coincides with the rotating axis of the centering spindle. With unfavorable lens shapes, however, when there is no self-centering effect of the centering bells, the lenses have to be centered in a separate centering device by means of a light ray before they are cemented to a centering spindle, set into rotation by means of this spindle and ground at their outer rim in order that the optical axis of the lens coincides with its geometrical axis.
A disadvantage of the procedure employed by the prior art for manufacturing lenses is that two grinding machines and a centering machine are required, in addition to the polishing machine. This represents the most modem known technology and under the further assumption that coarse grinding and precision grinding of each side of the lens is already done in a single device. Nevertheless, a large amount of machinery is involved. Another disadvantage of the prior art is that by means of the metal tools used therein, e.g., the above noted centering bells, the polished lenses are chucked in the centering machine at their delicate polished surfaces, which thus may be easily damaged.
Moreover, it is disadvantageous that with the conventional procedure described above, each lens is chucked at its circumference which has only the quality and precision of a glass blank. When the first lens side has been finished, the lens is turned about as hereinabove described and rechucked in a second device. During this rechucking and centering at the still little precise circumference of the lens, undesirable inaccuracies and differences between the optical axes of the two lens sides may occur.
It is an important object of the present invention to manufacture lenses more cheaply and, at the same time, to increase the processing accuracy. Additionally, the proposed procedure and the device for its implementation aim at simplifying coarse grinding and precision grinding of the two lens sides as well as simplifying centering operations.